Parallel optical communications modules have a plurality of optical channels, each of which includes a respective optoelectronic element that is optically aligned with an end of a respective optical waveguide or fiber. The parallel optical communications module may be a parallel optical transceiver module having both transmit and receive optical channels, a parallel optical transmitter module having only transmit optical channels, or a parallel optical receiver module having only receive optical channels. The optoelectronic elements are either light sources (e.g., laser diodes or light-emitting diodes (LEDs)) or light detectors (e.g., P-intrinsic-N (PIN) photodiodes). The optical fibers are either multi-mode optical fibers or single-mode optical fibers.
Multi-mode fibers are typically used in shorter network links whereas single-mode fibers are typically used in longer network links that have higher transmission bandwidths. The diameter of the light-carrying core of a typical single-mode fiber is between about 8 and 10 micrometers (microns) whereas the diameter of the light-carrying core of a typical multi-mode fiber is about 50 microns or greater. For this reason, active alignment techniques are typically used to align single-mode fibers with their respective light sources. Passive alignment techniques have been used to align multi-mode fibers with their respective light sources. In optical receivers, the apertures of photodiodes are decreasing in size due to requirements for higher speed, which is making it increasingly difficult to use passive alignment devices and techniques to precisely align the apertures of the photodiodes with the ends of multi-mode fibers.
Active alignment techniques typically involve using a machine vision system to align the fibers with their respective light sources and test and measurement equipment to test and measure the optical signal launched into the optical fiber by the light source as the optical signal passes out of the opposite end of the fiber. By using these active alignment techniques and equipment, a determination can be made as to whether the light source and the optical fiber are in precise alignment with one another.
Passive alignment techniques are performed without the laser being turned on. Typically, passive alignment is accomplished by aligning the component with a vision system and a precision alignment stage. Passive alignment can also be performed by mating a connector module that holds the ends of the optical fibers with the parallel optical communications module. Mating features on the connector module and on the parallel optical communications module ensure that the act of mating them brings the ends of the fibers into precise alignment with the respective light sources. When multi-mode optical fibers are used, such passive alignment techniques can provide sufficient alignment precision due to the relaxed alignment tolerances associated with the relatively large diameter of the fiber core.
Active alignment processes are much more costly and time consuming to perform than passive alignment processes and are difficult to perform in the field. Accordingly, it would be desirable to provide a parallel optical communications module that enables ends of a plurality of optical fibers or waveguides to be precisely passively aligned without turning on the respective optoelectronic elements (e.g., light sources and light detectors) of the module. Furthermore, it is desirable to provide a mechanism for alignment without having to use a vision system and precision alignment stage.